The present invention relates to data communications equipment and, more particularly, to the simultaneous establishment of voice and data calls using a modem pool and private branch exchange facilities.
The co-pending, commonly assigned, U.S. Patent application of Gordon Bremer et al. entitled "Simultaneous Analog and Digital Communication," serial No. 08/076505, filed on Jun. 14, 1993, describes a simultaneous voice and data communications system in which a voice signal is added to a data signal for transmission over a communications channel to a receiving modem.
In this simultaneous analog and digital communication system, the data signal to be transmitted is represented by a sequence of data symbols, where each data symbol is associated with a particular N-dimensional signal point value taken from a signal space. Similarly, the analog signal, which is represented by a voice signal, is processed so that it is mapped into the N-dimensional signal space to provide a voice signal point. This voice signal point defines the magnitude and angle of a voice signal vector about the origin of the signal space. The data symbol and the voice signal vector are then added together to select a resultant N-dimensional signal point, which is then transmitted to a far-end modem.
Upon reception of the transmitted N-dimensional signal point, the receiver of the far-end modem detects the embedded data symbol and subtracts the data symbol from the received N-dimensional signal point to yield the voice signal vector. This voice signal vector is then used to recreate the voice signal.
As a result, this simultaneous voice and data transmission technique advantageously provides a voice-band signal that has both an audio portion and a data portion. This allows two users with simultaneous voice and data (SVD) capable modems to communicate data between them and talk at the same time--yet only requires one "tip/ting" type telephone line at each user's location. However, in a typical corporate environment voice and data communications are not yet integrated. Indeed, voice and data facilities are usually provided to the corporation's employees over physically separate wiring, where the voice communications is typically switched through a private branch exchange (PBX) and the data communications may be over a local area network (LAN). Consequently, when a corporate user makes a voice call, that voice call is directly switched through the PBX, and if an outside call, through the public switched telephone network (PSTN), to the called party. Similarly, if the corporate user makes a data call, that data call is switched through a modem-pool to the PBX. A modem pool is a data resource that is coupled to the PBX and shared among a group of individuals. This allows the corporation to provide its employees with access to data services without having to dedicate a modem to each employee. The end result is that in this type of telecommunications environment, a corporate user cannot directly connect their telephone to an SVD capable modem to establish a simultaneous voice and data connection with another SVD user.